1. Field of the Invention
The present invention relates to a spin high-frequency mixer which uses spin torque, and a method of manufacture thereof.
2. Related Background Art
Advances have been made recently in information communications technology that uses radio waves of higher frequencies, such as wide-band code division multiple access (CDMA) using frequencies in the 2 GHz band, Bluetooth using frequencies in the 2.4 GHz band, and wireless LANs using even higher frequency waves.
In the terminals and in the equipment used in wireless base stations that are employed for such information communications, it is common for radio waves received from an antenna, for example, to be converted into lower frequency signals. In such cases, a high-frequency mixer circuit that employs a differential amplifier circuit is used to convert high-frequency signals into lower frequency signals.
An example of prior art which uses such as a high-frequency mixer circuit is the active mixer disclosed in Japanese Patent Application Laid-open No. H08-204458. This disclosure describes an high-frequency mixer having a field effect transistor (FET) that inputs high-frequency signals (RF signals) to a drain, inputs local oscillator (LO) signals to a gate, and extracts intermediate frequency (IF) signals from a source.
However, in an active mixer such as a high-frequency mixer disclosed in Japanese Patent Application Laid-open No. H08-204458, RF signals and LO signals are mixed using the field effect transistor. Because this field effect transistor is required to have both high-frequency characteristics and low-frequency characteristics, it is difficult to suppress low-frequency flicker noise. As a result, the noise characteristics are inferior to those of a passive mixer.
At the same time, passive mixers are devices which employ the non-linearity of a diode; with the LO signal as a bias, current flows to the diode, and the corresponding change in the differential resistance of the diode is used. Also, in order to use the non-linearity of the diode, the change in resistance must be made sufficiently large. Along with this, the current due to the LO signal must be increased to some degree. However, increasing the current causes shot noise due to the current to appear in the output. Hence, the noise cannot be reduced to a sufficient degree even with a passive mixer that uses a diode.